Hot wire anemometer was invented in the 1920s, the need to put a thin metal wire in the fluid, through the current heating wire, the temperature is higher than the fluid temperature, so the wire is called the "hot wire." Hotline length is generally 0.5 to 2 mm range, the diameter of 1 to 10 microns, the material is platinum, tungsten or platinum and rhodium alloys. If a very thin (less than 0.1 microns thick) metal film instead of metal wire, hot film anemometer, the function and hot wire similar, but more for the measurement of liquid flow rate. Hotline in addition to the ordinary single-line, but also can be a combination of two-wire or three-wire, to measure the speed component in all directions. The electrical signal output from the hotline can be amplified, compensated and digitized and then input into the computer to improve the measurement accuracy, automatically complete the data post-processing process and expand the speed measurement function. For example, the instantaneous value and hourly mean value, the combined speed and the minute speed, the turbulence degree And other measurements of turbulence parameters.

The basic principle of a hot wire anemometer is that a thin wire heated by electricity (called a hot wire) is placed in the air flow. The amount of heat dissipated by the hot wire in the air flow is related to the flow rate, and the heat dissipation causes and flows through the temperature change of the hot wire Current intensity, ΔT is the temperature difference between the fluid and the fluid, A, B and fluid and hot-line-related physical constants. Taking into account the temperature characteristics of the hot wire material, (D3.4.4a) can be transformed into (D3.4.4b).

In the above formula, U is the output voltage of the hot line, and A 'and B' are the physical constants related to the temperature coefficient of resistance of the hot line, which are determined experimentally. This determines the flow rate by measuring the voltage across the hotline.

1. Small size, small disturbance to the flow field.

2. Wide range of applications, can be used for gases, liquids, in the gas subsonic, transonic and supersonic flow can be used; In addition to measuring the average speed, but also measure the value of the pulsation and turbulence; In addition to measuring unidirectional motion Speed components in multiple directions can be measured at the same time.

3. High frequency response, up to 1 MH z.

4 measurement accuracy, good repeatability.

5. The disadvantage is that the flow field has some interference, the hotline is easy to break.